The inks used to provide either decorative functionality (black-out, fade-out, logo, etc.) or conductive functionality (defroster, antenna, etc.) for plastic automotive windows are typically applied directly to the window surface and subsequently over-coated with protective (weathering, abrasion resistant) coatings. However, this may lead to the creation of optical distortion at the edges of the printed image. For example, along each of the grid lines that make up the defroster grid pattern, this optical distortion may affect the driver's field of vision.
As shown for part 10 of FIG. 1, a cause of this optical distortion is believed to be related to the difference in coating thickness that occurs across a substrate 12 of the part 10 and at the interface between a printed image 14 and the remaining surface of the part 10. As shown in FIG. 1, the thickness of the coating system (referenced as layers 1-3) near the image-part interface, Athickness, can be substantially greater than the thickness of the coating over the rest of the part, Bthickness. The difference in the refractive index between the different coating layers causes light to be refracted differently in the two regions marked as light path A and light path B in FIG. 1. Thus, the human eye will detect an optical distortion near the printed image.
In view of the above drawbacks and other limitations of the prior art, it is seen that there exists a need for a printed plastic window panel that does not exhibit, or at least minimizes, optical distortion through the window.